Center lock devices for attaching an automobile wheel to an axle hub through a separate adapter in such a manner as to allow it to be removed for exchange and make torque transmission possible, wherein a center nut is threaded on the male thread portion of a center shaft which projects forward from the center of the adapter so as to lock the wheel disk against slip-off, are known as can be seen in French Patent No. 1504385 (corresponding to Japanese Patent Publication No. 18642/1971), Japanese Utility Model Application Laid-Open No. 38701/1978 and Japanese Utility Model Publication No. 16641/1989.
The known techniques mentioned above are basically the same in the arrangement in each of the above references and hence French Patent No. 1504385 mentioned above is taken up as an example for description. An adapter or sleeve 19 is formed with a male thread 21 and a single center nut 26 of the cap type is threadedly engaged directly with said male thread 21. Therefore, the advantage is that by simply turning the single center nut 26, the exchange of wheels can be effected as quickly as in the case of racing cars.
On the other hand, however, since the center nut 26 is a large-sized special part, a great force is required in tightening the male thread 21; it often happens that the resulting tightening is insufficient. Further, since the wheel disk 12 is pressed at the center by only one center nut 26 and thereby fixed in position, if the center nut 26 is repetitively subjected to vibrations or shocks caused by hard brakes or the like during traveling of the automobile, the center nut 26 can easily play or loosen.
Notwithstanding this, there has been no special means added thereto for preventing the loosening of the center nut 26, with the result that there is still some anxiety in the durability and safety of the wheel fixed in position and the stealing of wheels are often encountered.
On the other hand, the present inventor has already proposed U.S. Pat. No. 4,537,449 (corresponding to Japanese Patent Application Laid-Open No. 118502/1984) in order to improve French patent invention mentioned above and Japanese Utility Model Application Laid-Open No. 38701/1978 invented by the present inventor.
The above U.S. patent employs a commonplace bolt B and small-sized center nut N, making it possible to quickly exchange wheels using a relatively small tightening force while preventing the center of a wheel disk D from being visually hidden by the large center nut of the cap type and increasing the degree of freedom in giving various molding patterns for ventilation purposes to said wheel disk D.
However, according to the above-mentioned U.S. Patent, the center bolt B and center nut N are relatively small parts, they are singular, and there is no means specially provided for preventing the loosening of the center nut N; thus, as compared with said French patent invention, it causes the customers to harbor increasing uneasy feelings about the durability and safety of the wheel fixed in position and stealing. This is a serious problem in sales of spare wheels.
As for means for preventing the loosening of the center nut and the stealing of wheels in connection with such center lock device for automobile wheels, Japanese Patent Application Laid-Open No 190001/1984 has been proposed.
It provides a center lock device for automobile wheels, wherein the hub 6 of an axle 4 has joined thereto a seat plate 12 having a thick threaded sleeve 13 and the core hole 16 of a wheel disk 1 is fitted on the plain portion 14 of the threaded sleeve 13, with a cap nut (center nut) N threadedly applied thereto, so that the disk 1 is joined to the axle 4 by the seat plate 12 and cap nut N,
The center lock device is characterized in that it comprises an inner tooth ring 17 having teeth 18 cut around the entire periphery of the inner surface, said inner tooth ring being integrally formed on the mouth end of said threaded sleeve 13, a passage hole 22 formed in the end plate 20 of the cap nut N, said passage hole having attached to the inner surface thereof a lock main body 24 having an electronic lock L or cylinder lock built therein, the back surface of said lock main body 24 having a slot 30 in which are installed an intermediary lever 34 having pawls 35 meshing with the teeth 18 of the inner tooth ring 17 and push springs 33 for said pawls 35, a cam 33 for the electronic lock L or cylinder lock received in the middle of said slot 30 and contacted with the intermediary lever 34, said cam 33 serving to advance or retract the pawls 35 to cause the pawl tips to mesh with the inner tooth ring 17or disengage them from the latter.
With this arrangement, however, even if the loosening of the cap nut (center nut) N or the stealing of wheels can be prevented, the number of parts required for this purpose is very large, and the processing and assembling of such parts are very troublesome, such parts being finished as very expensive special parts; thus, such device cannot be easily obtained for use with spare wheels by general users or cannot be used with ease.